1. Field of the Invention
The present invention relates to a liquid ejection head and an image forming apparatus, and more particularly, to a liquid ejection head and an image forming apparatus which eject liquid from ejection ports connected to pressure chambers, by utilizing the displacement of piezoelectric elements.
2. Description of the Related Art
An inkjet recording apparatus is known which forms images on a recording medium by ejecting ink droplets from nozzles, while moving a print head (liquid ejection head) in which a plurality of nozzles are formed, relatively with respect to the recording medium. One ejection method for a print head installed in an inkjet recording apparatus of this kind is a piezoelectric method which ejects ink droplets from the nozzles connected to pressure chambers, by utilizing the displacement of piezoelectric elements to change the volume of pressure chambers filled with ink, thereby pressurizing the ink filled into the pressure chambers.
Japanese Patent Application Publication Nos. 8-58085 and 11-123821 disclose print heads in which pressure chambers, and piezoelectric elements disposed in positions opposing the ink supply flow channel and corresponding to these pressure chambers, are arranged respectively on either side of a diaphragm which constitutes a wall of the pressure chambers. In these print heads, during ink ejection, the cross-sectional area of the ink supply flow channel is reduced by the diaphragm due to the deformation of the piezoelectric element, thereby preventing reverse flow of the ink from the pressure chambers toward the common liquid chamber. However, in these print heads, the ink inside the pressure chambers is indirectly pressurized by means of a diaphragm, and hence there is a problem in that the ink ejection efficiency is poor in relation to the displacement of the piezoelectric elements.
Japanese Patent Application Publication No. 2-253962 discloses a print head in which the ink flow channel is divided into two sides by an elastic movable actuator having a cantilever beam structure, one side forming a nozzle side and the other side forming a flow channel side connecting to a common liquid chamber. In this print head, the ink is supplied to the nozzle side through a gap between the side wall of the ink flow channel and the elastic movable actuator. During refilling, the elastic movable actuator disposed inside the ink flow channel acts in a direction that increases the volume on the nozzle side, while during ink ejection, it acts in a direction that reduces the volume on the nozzle side. However, no consideration is given to the ink ejection efficiency with respect to the displacement of the elastic movable actuator.
Japanese Patent Application Publication No. 2001-334674 discloses a print head in which nozzles, pressure chambers (ink chambers) and a common liquid chamber (ink pool) are constituted by a single substrate, piezoelectric elements being disposed on the opposite side of the pressure chambers to the nozzle side, with the object of achieving an improvement in the reliability and production yield of the head, and reducing the size of the head. However, similarly to Japanese Patent Application Publication No. 2-253962, no consideration is given to the ink ejection efficiency.
Japanese Patent Application Publication No. 2004-237676 discloses a print head in which unimorph type piezoelectric elements are provided in the interior of pressure chambers. In this print head, piezoelectric elements are fixed to a diaphragm which constitutes an inner wall of the pressure chambers. In the piezoelectric element which makes contact with the ink in the pressure chamber, the displacement in the longitudinal direction, which is the liquid droplet ejection direction, and the displacement in the transverse direction which is perpendicular to this direction, are mutually conflicting, and therefore the ink ejection efficiency with respect to the displacement of the piezoelectric element is poor.